Anchors have been used for centuries and generally comprise two essential elements: a shank and at least one fluke. To properly function, the fluke(s) should engage the bottom of the body of water, such as a lake bottom or a sea floor. The fluke is generally secured to one end of the shank. The other end of the shank is joined to a cable which, in turn, is tied to the craft.
Beyond these essential common elements, anchor designs vary widely. One reason for the variety of anchor designs is the variety in the types of bed soil conditions that are encountered in moorings. Thus, soils may be sandy, rocky, hard or soft, have plant growth, or any combination of these soil conditions. One previous anchor which was designed to engage all types of soil conditions satisfactorily was disclosed in my U.S. Pat. No. 4,418,635, incorporated herein by reference.
While the design the '635 patent was effective in engaging the various types of soil commonly encountered in moorings, it did not solve all the drawbacks of previous anchor designs. Anchor designs prior to that of the '635 patent shared an inherent flaw, the inability to bite through the first layers of bottom material to the more finely compacted composition below that provides greater holding power. The overlying material often contains grass, weed, coral and shell parts, and other loose debris that provide little or no holding force for an anchor, while the material below provides much greater holding force. Previous anchor designs had trouble penetrating the overlying layer due to the position of the shank, which on prior anchor designs was placed at the center of the anchor's flukes. As the center-shanked anchor is setting, the shank attempts to divide the mass of bottom material equally as it is supplied by the anchor's flukes. This inevitably results in the accumulation of incompatible bottom material at the shank in interfering with penetration to the better holding hardpack below.
The anchor of the '635 patent was designed with the shank away from the fluke to help avoid the predisposition to clog, yet retain balance under load so the anchor would not "roll out" but remain oriented to penetrate through the poor holding overlying bottom material. The triangle-shaped fluke of that anchor achieved its goal to feed through poor holding bottom material but because the center of gravity or center of effort of the triangle fluke was off-center of the preferred maximum resistance orientation of perpendicular, an adverse side effect was created. This is the tendency to "crab" or move diagonally through the bottom from the load imposed by the water craft. This lessened holding power as the triangular fluked anchor of the '635 patent "slipped" or clutched", allowing the craft to move back and away, commonly called "dragging" in the art. The triangular shaped fluke also restricted the fluke area by limiting its size.
Any increase in size or extension of the triangle only moves the center of effort further from perpendicular, thereby exaggerating the diagonal movement. The limited size of the triangular fluke also impairs proper penetration in softer bottoms such as mud and grainy sand as the resistance in these bottoms is insufficient to pull the anchor further down to better holding bottom compositions without an adequate amount of fluke area to create enough resistance to facilitate further penetration.
This phenomenon therefore dictates a certain tradeoff, the fluke must be made large enough to provide sufficient surface area for adequate holding power, but the greater the surface area of the triangular fluke the greater the tendency to crab. Thus, there remains a need for a fluke that can provide the necessary large surface area while eliminating the side force generated by the triangular fluke.